Thin Wall Active Casing Hanger

ABSTRACT

A wellbore system includes a housing assembly and first and second position casing hangers supported by the housing assembly. A load member is provided that is adapted to extend between the first position casing hanger and the housing assembly to enable the housing assembly to support the first position casing hanger. The second position casing hanger is stacked onto the first position casing hanger, and an interface is defined between the first and second position casing hangers to aid in alignment and centralization of the second position casing hanger during installation. The interface also provides radial support to the first position casing hanger and enables loads associated with the second position hanger to be transferred to the housing assembly through the load member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to mechanisms for supporting acasing string from a wellhead. More specifically, the invention relatesto a stacked casing hanger assembly for providing a load capacity in acompact space while facilitating installation.

2. Description of the Related Art

In an oil or gas well, a wellhead will generally be located on theground surface, or on the sea floor for a subsea well. The wellhead is atubular member having an axial bore. At least one load shoulder isusually disposed within the bore for supporting casing string. In deepwells, there will generally be more than one casing string extendinginto the well, and one or more load shoulders may be provided forsupporting each one of the casing strings.

Often, once a well is drilled to a certain depth, a first casing stringis lowered through the axial bore of the wellhead and supported by afirst casing hanger on a first load shoulder in the wellhead. Cement ispumped down the first casing string and back up an annulus surroundingthe first casing string to cement the first casing string within thewell. The well may then be drilled to deeper depths at a smallerdiameter, and a second casing string may be lowered through the wellheadand the first casing string to extend below the first casing string. Asecond casing hanger at the top of the second casing string maypositioned in the wellhead and supported by an upper surface of thefirst casing hanger. In some techniques, the entire weight of the secondcasing string and second casing hanger is transmitted through the firstcasing hanger to the first load shoulder. In other techniques, a secondload shoulder is provided to support a portion of the weight of thesecond casing string while a portion of the weight is also transmittedthrough the first casing hanger to the first load shoulder. The secondcasing string may then be cemented into place,

In addition to supporting the weight of the casing strings, the casinghangers must also generally support high pressures from tests ofequipment placed above the casing hangers, and working loads associatedwith producing from the well. For at least this reason, casing hangersmust be fairly robust. Casing hangers must also generally provide alarge drift size to permit passage of additional casing strings,drilling implements or other equipment therethough. To allow for thepassage of larger pieces of equipment, walls of the casing hangers arethin, which may limit the load carrying capacity of a casing hanger insome instances.

SUMMARY OF THE INVENTION

Described herein is a wellbore system including first and secondposition casing hangers supported in a wellhead. A load member isprovided that is adapted to extend between the first position casinghanger and the housing assembly to enable the housing assembly tosupport the first position casing hanger. The second position casinghanger is stacked onto the first position casing hanger, and aninterface is defined between the first and second position casinghangers at a longitudinal elevation of the load member to provide radialsupport to the first position casing hanger. The interface also aids inalignment and centralization of the second position casing hanger duringinstallation.

According to one aspect of the invention, a wellhead system includes awellhead with a bore. A first position casing hanger is in the bore andincludes an upper end, a lower end and an axial passage. The lower endof the first position casing hanger includes a first connector connectedto a first casing string. A second position casing hanger is in the boreand includes an elongated annular body that extends into the axialpassage of the first position casing hanger, and a second connectorconnected to a second casing string. A centralizing ring is set in anannular space between the elongated annular body and the first positioncasing hanger, so that when the first position casing hanger deflectsradially inward in response to axial loads, the centralizing ringsupports the first position casing hanger.

According to another aspect of the invention, a wellhead system includesa wellhead housing, an upper hanger mounted in an axial bore in thewellhead housing, and a lower hanger mounted in the axial bore andcircumscribing the upper hanger. The lower hanger includes sidewallsthat deflect radially inward in response to axial loading of the upperhanger. A centralizing ring is strategically disposed adjacent to wherethe sidewalls deflect and between the upper and lower hangers.

According to another aspect of the invention, a wellhead system includesa wellhead with an axial bore, a first position casing hanger in thebore and comprising an axial passage, a first casing string connected tothe first position casing hanger, a second position casing hanger in thebore and comprising an elongated annular body that extends into theaxial passage of the first position casing hanger, a second casingstring connected to the second position casing hanger, and acentralizing ring in an annular space between the elongated annular bodyand the first position casing hanger, so that when the first positioncasing hanger deflects radially inward in response to axial loads, thecentralizing ring supports the first position casing hanger. Thewellhead system also includes an annular load ring comprising an innerprofiled circumference that engages an outer surface of the firstposition casing hanger, and an outer profiled circumference that engagesan inner surface of the wellhead within the axial bore to define alongitudinal support region. A first channel in the wellhead intersectsthe axial bore above and below the longitudinal support region.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features, aspects andadvantages of the invention, as well as others that will becomeapparent, are attained and can be understood in detail, a moreparticular description of the invention briefly summarized above may behad by reference to the embodiments thereof that are illustrated in thedrawings that form a part of this specification. It is to be noted,however, that the appended drawings illustrate only preferredembodiments of the invention and are, therefore, not to be consideredlimiting of the invention's scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a partial cross-sectional view of a wellhead system includinga stacked casing hanger assembly including first and second positioncasing hangers installed in a high pressure wellhead in accordance withone example embodiment of the present invention.

FIG. 2 is a detailed cross-sectional view an interface between the firstand second position hangers as identified as an area of interest in FIG.1.

FIG. 3 is an end view of the stacked casing hanger assembly of FIG. 1.

FIG. 4 is an end view of an alternate stacked hanger assembly inaccordance with another embodiment of the present disclosure.

FIG. 5 is a simplified representation of example loading conditionsapplied to the wellhead system of FIG. 1, which includes first andsecond position casing hangers having the interface of FIG. 2established therebetween.

FIG. 6 is a simplified representation of an alternate wellhead systemincluding first and second position casing hangers, which do not havethe interface of FIG. 2 established therebetween.

FIG. 7 is a chart indicating the longitudinal displacement of the firstposition casing hangers of FIGS. 5 and 6 resulting from loading thefirst position casing hangers as indicated in FIGS. 5 and 6.

FIG. 8 is a chart indicating the radial displacement of the firstposition casing hangers of FIGS. 5 and 6 resulting from loading thefirst position casing hangers as indicated in FIGS. 5 and 6.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Referring generally to FIGS. 1 and 2, a wellhead system 10 includes awellhead housing assembly 12 and a stacked casing hanger array 14supported therein. The wellhead system 10 defines a longitudinal axisA_(X) extending therethrough. As used herein, the terms “longitudinal”and “axial” or variants thereof generally describe a direction parallelto the longitudinal axis A_(X), and the term “radial” or variantsthereof generally describes a direction that is substantiallyperpendicular to the longitudinal axis A_(X).

The wellhead housing assembly 12 includes an outer housing 18 and a highpressure housing or high pressure wellhead 20 having an axial bore 22.The stacked casing hanger array 14 is an arrangement of two casinghanger assemblies 26, 28 including a first position casing hanger 26 anda second position casing hanger 28. The second position casing hanger 28is “stacked” on the first position casing hanger 26 as described ingreater detail below. In this example embodiment, a lockdown bushing 29is optionally disposed above the second position casing hanger 28. Inother embodiments (not shown), additional casing hanger assemblies maybe stacked on the second position casing hanger 28.

The stacked casing hanger array 14 is supported in the axial bore 22 byengagement between a load member 30 and the high pressure wellhead 20.In this example embodiment, the load member 30 is an inwardly-biased,expandable C-ring that is installed on the first position casing hanger26 prior to installation into the high pressure wellhead 20. Onceinstalled in the high pressure wellhead 20, the load member 30 interactswith an actuation member 32 such that the load member 30 expandsradially outwardly to extend between the first position casing hanger 26and the high pressure wellhead 20. The engagement of load member 30 withthe high pressure wellhead 20 is described in greater detail in commonlyowned, U.S. application Ser. No. 12/415,198 to Nicholas P. Gette et al.,filed Mar. 31, 2009, the entire disclosure of which is herebyincorporated by reference herein for all purposes.

The high pressure wellhead 20 as shown includes a toothed profile 34 inthe axial bore 22, which defines a plurality of upward-facing shoulders36. A corresponding exterior toothed profile 40 is provided on the loadmember 30, which is received in the toothed profile 34 of the highpressure wellhead and supported on the upward-facing shoulders 36. Thefirst position casing hanger 26 also includes a toothed profile 44having downward-facing shoulders 46. A corresponding interior toothedprofile 48 on the load member 30 is received within the toothed profile44 of the first position casing hanger 26, and engages thedownward-facing shoulders 46 to support the first position casing hanger26.

The high pressure wellhead 20 also includes a plurality of channels 50defined therein extending from a port 52 disposed above the toothedprofile 34 and a port 54 disposed below the toothed profile 54 and theactuation member 32. The ports 52, 54 provide fluid communicationbetween the axial bore 22 of the high pressure wellhead 20 and thechannels 50 to permit drilling mud, cement or other well fluids to passthrough the wellhead system 10, and bypass the interface between toothedprofile 34 and toothed profile 44.

The first position casing hanger 26 includes a threaded lower end 60,which provides a connector from which a first casing string 61 issuspended. An upper end 62 of the first position casing hanger 26provides a circumferential shelf 64 extending around an axial passage 66extending longitudinally through the first position casing hanger 26.The second position casing hanger 28 is supported by the circumferentialshelf 64 and extends into the axial passage 66.

Still referring to FIGS. 1 and 2, the second position casing hanger 28includes a threaded lower end 70 from which a second casing string 71 issuspended. An elongated body 72 of the second position casing hanger 28is received within the axial passage 66 of the first position casinghanger 26 and extends longitudinally through the toothed profile 44. Anupper end 74 of the first position casing hanger 28 extends radiallyoutward from the elongated body 72 and includes a downward-facing ledge76. The downward-facing ledge 76 abuts the circumferential shelf 64 onthe first position casing hanger 26 to support the second positioncasing hanger 28. The upper end 74 of the second position casing hanger28 extends radially to the high pressure wellhead 20. In the exampleembodiment depicted in FIG. 1, the upper end 74 is devoid of a loadmember for supporting the second position casing hanger 28 directly fromthe high pressure wellhead 20. In other embodiments (not shown) a loadmember may be provided on the upper end 74. Channels 78 are providedthrough the upper end 74 of the second position casing hanger 28 toprovide fluid communication between the axial bore 22 of the highpressure wellhead 20 and the axial passage 66 of the first positioncasing hanger 26. An axial bore 80 extends longitudinally through thesecond position casing hanger 28.

A centralizing ring 82 is provided on the second position casing hanger28, and extends radially outward from an exterior surface 84 of theelongated body 72. The centralizing ring 82 is provided at alongitudinal distance from the downward-facing-ledge 76 such that whenthe second position casing hanger 28 is installed into the wellheadsystem 10, the centralizing ring 82 is disposed at a longitudinalelevation of at least one of the upward-facing shoulders 36, and betweenupper and lower ends of the load ring 30 and toothed profiles 34, 44.Thus, the centralizing ring 82 is disposed within a longitudinal supportregion “R;” which defines an axial distance where the first positioncasing hanger 26 engages the high pressure wellhead 20. The weight ofthe first position casing hanger 26 and any weight suspended therefromis transferred to the high pressure wellhead 20. Opposing axial surfacesof the centralizing ring 82 are profiled to define a lower taper 85 andan upper taper 86, which project obliquely to a circumferential supportsurface 88. The support surface 88 is substantially parallel to axisA_(X), and corresponds with a shape of the axial passage 66 of the firstposition casing hanger 26. The centralizing ring 82 extends into theaxial passage 66 of the first position casing hanger 26 such that anannular clearance “C” is defined between the circumferential supportsurface 88 and a wall of the axial passage 66. In this exampleembodiment, the annular clearance “C” is about 0.015 inches. In otherembodiments (not shown) the centralizing ring 82 is configured toprovide any slightly positive annular clearance “C.” For example,clearances “C” in the range of about 0 to about 0.125 inches areprovided in some embodiments. In other embodiments, a slightly negativeannular clearance “C,” i.e., a slight interference fit may beestablished between the support surface 88 and the first position casinghanger 26.

As depicted in FIG. 3, the centralizing ring 82 includes a plurality ofsegments 82A, spaced around the second position casing hanger 28. Eachof the segments 82A extend radially outward from the exterior surface 84of the second position casing hanger 28 to the support surface 88. Thesupport surface 88 is generally shaped to correspond to the shape of theaxial passage 66 of the first position casing hanger 26. Flow channels66A are defined in the axial passage 66 of the first position hanger 26between the segments 82A. In this embodiment, flow channels 66A occupyabout half a cross-sectional area of an annulus defined between theexterior surface 84 and the first position casing hanger 26, with thesegments 82A occupying the other half. The flow channels 66A interruptthe support surface 88. As described in greater detail below, thesupport surface 88 provides radial support to the first position casinghanger 26.

In an example of operation, a wellbore is drilled to a first depth andthe high pressure housing 20 is installed. The first position casinghanger 26 is installed in the high pressure housing 20 with the firstcasing string 61 suspended therefrom. The weight applied by the firstposition casing hanger 26 on the load ring 30 causes the load ring 30 toengage the actuation member 32 and radially expand to transfer theweight of the first casing string 61 to the high pressure housing 20.Prior to installation of the second position casing hanger 28, the axialpassage 66 of first position casing hanger 26 provides a relativelylarge passageway into the wellbore (for passage of drill bits anddrilling equipment, surveying or test devices, etc.) in comparison toconventional casing hangers with similar nominal sizes. The axialpassage 66 has a relatively large diameter, since a wall thickness “T”of the first position casing hanger 26 is relatively small. The wallthickness “T” is relatively small since first position casing hanger 26does not need to support the weight of both casing strings 61, 71 alonesince the centralizing ring 82 provides radial support to the firstposition casing hanger 26 once loaded with the weight of the secondcasing string 71. Thus, prior to installation of the second positioncasing hanger 28, the first position casing hanger 26 allows relativelylarge equipment to be lowered into the wellbore and provides operatorswith options that might not be available with a smaller axial passage66.

After the first position casing hanger 26 is installed, the wellbore isdrilled to a second depth, and the second position casing hanger 28 islowered into the axial passage 66 with the second casing string 71suspended therefrom. As the centralizing ring 82 passes thecircumferential shelf 64 on the first position casing hanger 26, thelower taper 85 guides the elongated body 72 of the second positioncasing hanger 28 into a central location within the axial passage 66.The downward-facing ledge 76 rests on the circumferential shelf 64 suchthat the weight of the second casing string 71 is transferred to thefirst position casing hanger 26 and to the high pressure wellhead 20through the load ring 30. As a result of the weight of the first andsecond casing strings 61, 71 as well as axial forces associated withtesting performed above the first position casing hanger 26, e.g., apressure test of a blow-out preventer (not shown), the first positioncasing hanger 26 is elastically or plastically deformed to exhibitradial inward displacements. The support surface 88 on the centralizingring 82 provides radial support to the first position casing hanger 26,such that the first position casing hanger 26 may support larger axialloads than the first position casing hanger 26 would otherwise supportin the absence of centralizing ring 82.

As depicted in FIG. 4, an alternate embodiment of a centralizing ring 90provides a continuous support surface 92 that extends circumferentiallyaround the entire centralizing ring 90. Bores 94 extend longitudinallythrough the centralizing ring 90 to provide fluid communication throughthe centralizing ring 90.

Referring now to FIGS. 5 and 6, example loading conditions areillustrated on a simplified depiction of the wellhead system 10 (FIG.5), which includes a centralizing ring 82, and on an alternateembodiment of a wellhead system 100 (FIG. 6), which is devoid of, acentralizing ring. The example loading conditions were utilized by afinite element analysis to describe the expected stresses and strain onvarious components of the wellhead systems 10, 100. Example results ofthe finite element analysis are illustrated in FIGS. 7 and 8.

An axial constraint AC1 is assigned to the high pressure wellhead 20 ona lower socket surface thereof. The axial constraint AC1 represents areference location on the wellhead systems 10, 100 from which relativedisplacements of the various components of the wellhead systems 10, 100are measured as the first position casing hanger 26 is loaded. An axialconstraint AC2 is also applied to an upper surface of the secondposition casing hangers 28 (FIGS. 5) and 102 (FIG. 6). Although someaxial displacement may be expected in the upper surfaces of the secondposition the casing hangers 28, 102, for the purpose of analysis, theaxial constraint AC2 maintains the second position casing hangers 28,102 in an approximate position where the centralizing ring 82 is axiallybetween upper and lower ends of the load ring 30. A first load MPC-1 isapplied to the lower end 60 of the first position casing hanger 26,which represents the weight of a first casing string 61 (FIG. 1)suspended from the first position casing hanger 26. A second load MPC-2is applied to the circumferential shelf 64 of the first position casinghanger 26 and represents the weight of a second casing string 71(FIG. 1) suspended from the second position casing hanger 28, as well asforces applied to the first position casing hanger 26 from testingperformed above the first position casing hanger 26.

Referring now to FIGS. 7 and 8, together with FIGS. 5 and 6, the axialand radial displacements of the first position casing hanger 26 areplotted against the axial load applied to the first position casinghanger 26. Lines L1 and L3 correspond to the wellhead system 10 (FIG.5), and represent the displacements of a point “U” on the first positioncasing hanger 26, which is adjacent the centralizing ring 82. Lines L2and L4 correspond to the wellhead system 100 (FIG. 6) and represent thedisplacements of the point “U” on the first position casing hanger whencentralizing ring 82 is not provided. The first load MPC-1 of 2 millionpounds of casing weight applied to the lower end 60 of the firstposition casing hanger 26 induces a 0.28 inch axial displacement ofpoint “U” as represented at point A₀ (FIG. 7) and a 0.0056 inch inwardradial displacement of point “U” at point B₀ (FIG. 8). At a loading of 2million pounds, the axial and radial displacements of the point “U” arethe same for the wellhead system 10, which includes the centralizingring and the wellhead system 100, which is devoid of a centralizingring.

A divergence is observed at points A₁ and B₁ where the second load MPC-2of 6.76 million pounds is applied to the circumferential shelf 64 of thefirst position casing hanger 26. At point A₁, a 0.28 inch axialdisplacement of point “U” is observed, and at point B₁, a 0.0165 inchradial displacement is observed. The 0.0165 inch radial displacement atpoint B₁ is greater than the 0.015 inch the clearance “C” definedbetween the support surface 88 of the centralizer ring 82 and the firstposition casing hanger 26. Thus, the point “U” contacts the supportsurface 88 of the centralizer ring 82, and the centralizer ring 82provides radial support to the first position casing hanger 26.Additional loads applied to the first position casing hanger 26 inducelower axial and radial displacements at point “U” in wellhead system 10where the centralizer ring 82 is provided than in wellhead system 100where the centralizer ring is not provided. The additional loads appliedto the first position casing hanger 26, that generate the axial andradial displacements plotted in FIGS. 7 and 8 (above points A₁ and B₁)are applied to the lower end 60 and the circumferential shelf 64 of thefirst position casing hanger 26 in proportion to the 2 million poundMPC-1 and the 6.76 million pound MPC-2.

The present invention described herein, therefore, is well adapted tocarry out the objects and attain the ends and advantages mentioned, aswell as others inherent therein. While a presently preferred embodimentof the invention has been given for purposes of disclosure, numerouschanges exist in the details of procedures for accomplishing the desiredresults. These and other similar modifications will readily suggestthemselves to those skilled in the art, and are intended to beencompassed within the spirit of the present invention disclosed hereinand the scope of the appended claims.

What is claimed is:
 1. A wellhead system comprising: a wellhead with abore; a first position casing hanger in the bore and comprising an upperend, a lower end, and an axial passage, the lower end of the firstposition casing hanger including a first connector connected to a firstcasing string; a second position casing hanger in the bore andcomprising an elongated annular body that extends into the axial passageof the first position casing hanger, and a second connector connected toa second casing string; and a centralizing ring set in an annular spacebetween the elongated annular body and the first position casing hanger,so that when the first position casing hanger deflects radially inwardin response to axial loads, the centralizing ring supports the firstposition casing hanger.
 2. The wellhead system of claim 1, wherein thefirst position casing hanger is supported by at least one upward-facingshoulder defined within the bore of the wellhead, and wherein thecentralizing ring defines a support surface that is disposed at alongitudinal elevation of the at least one upward-facing shoulder. 3.The wellhead system of claim 2, wherein the at least one upward-facingshoulder comprises a toothed profile that selectively receives a radialexpandable load member therein, and wherein the support surface of thecentralizing ring is disposed longitudinally between upper and lowerends of the toothed profile.
 4. The wellhead system of claim 1, whereinthe first position casing hanger includes a circumferential shelfextending around an upper end thereof, wherein the second positioncasing hanger includes an upper end extending radially outward from theelongated annular body and defining a downward-facing ledge thereon, thedownward-facing ledge abutting the circumferential shelf to support thesecond position casing hanger.
 5. The wellhead system of claim 1,wherein an annular space is between a support surface of thecentralizing ring and the first position casing hanger when the firstposition casing hanger is unloaded.
 6. The wellhead system of claim 1,wherein an interference fit is established between a support surface ofthe centralizing ring and the first position casing hanger when thefirst position casing hanger is unloaded.
 7. The wellhead system ofclaim 1, wherein the axial passage selectively receives a drill bitprior to installation of the second position casing hanger.
 8. Thewellhead system of claim 1, wherein the centralizing ring includes alower taper extending between an exterior surface of the elongatedannular body and a support surface defined at a radially outer edge ofcentralizing ring for guiding the second position casing hanger to acentral location with respect to the axial passage of the first positioncasing hanger.
 9. The wellhead system of claim 1, wherein thecentralizing ring includes a plurality of radially spaced segmentsdefining flow channels therebetween, and wherein a support surfacedefined around an outer periphery of the centralizing ring isinterrupted by the flow channels.
 10. The wellhead system of claim 9,wherein the flow channels occupy about half a cross-sectional area of anannulus defined between an exterior surface of the elongated body andthe first position casing hanger.
 11. The wellhead system of claim 1,wherein the centralizing ring defines a continuous support surfacecircumscribing the centralizing ring, and where at least one boreextends longitudinally through the centralizing ring to provide fluidcommunication through the centralizing ring.
 12. A wellhead systemcomprising: a wellhead housing; an upper hanger mounted in an axial borein the wellhead housing; a lower hanger mounted in the axial bore andcircumscribing the upper hanger, and comprising sidewalls that deflectradially inward in response to axial loading of the upper hanger; and acentralizing ring strategically disposed adjacent to where the sidewallsdeflect and between the upper and lower hangers.
 13. The wellhead systemof claim 12, wherein the upper hanger is stacked onto the lower hangersuch that weight suspended from the upper hanger is transferred to thelower hanger.
 14. The wellhead system of claim 12, wherein thecentralizing ring includes a longitudinally elongated support surfacedefined at a radially outer edge thereof.
 15. The wellhead system ofclaim 12, wherein the centralizing ring is strategically disposed in alongitudinal support region from which a weight suspended from the firsthanger is transferred to the wellhead housing.
 16. The wellhead systemof claim 12, wherein at least one fluid flow channel extendslongitudinally through the centralizing ring.
 17. A wellhead system,comprising: a wellhead with an axial bore; a first position casinghanger in the bore and comprising an axial passage; a first casingstring connected to the first position casing hanger; a second positioncasing hanger in the bore and comprising an elongated annular body thatextends into the axial passage of the first position casing hanger; asecond casing string connected to the second position casing hanger; acentralizing ring in an annular space between the elongated annular bodyand the first position casing hanger, so that when the first positioncasing hanger deflects radially inward in response to axial loads, thecentralizing ring supports the first position casing hanger; an annularload ring comprising an inner profiled circumference that engages anouter surface of the first position casing hanger, and an outer profiledcircumference that engages an inner surface of the wellhead within theaxial bore to define a longitudinal support region; and a first channelin the wellhead that intersects the axial bore above and below thelongitudinal support region.
 18. The wellhead system of claim 17,further comprising a second channel in the second position casing hangerextending between the axial bore and the axial passage.